In sawmills various timber handling machinery is provided to cut and shape the timber into wood products such as veneers, board products and the like. In forming a board product, the tree or flitch material is cut to the desired cross section of the three dimensional shape desired for the lumber product being produced and the piece are then cut to length. When board lumber is handled within a mill, automation is generally provided throughout the mill to transport the material to be cut or worked within the sawmill. Frequently, the board lumber is transported from one work position to another on a flat bed roller system.
Once the flitch has been cut to the desired cross section, it is supplied to saw equipment for cutting to length. To cut the material to length, one arrangement of transport equipment has a conveyor that has a flat bed lug chain transport table to carry the lumber pieces toward the length cutting saws. The lumber pieces are carried along the conveyor in equidistantly spaced succession based on the lug spacing of the lug chains. The conveyor has a set of lateral alignment rollers. The lateral alignment rollers form a roller bed system placed at right angles to the lug chain, which operate to urge one end of the lumber material toward a stop or fence. In this arrangement, each successive piece of lumber is spaced from the other in the direction of travel along the lumber conveyor by the lugs of the lug chain and one of the ends of the lumber is laterally aligned to the stop or fence.
The piece to be cut to length is positioned for contact with a saw. In the configuration of sawmill conveyor equipment just described, the saw is stationary relative to the conveyor and the board is laterally positioned on the conveyor relative to the saw blade. A positioning fence, which one end of the lumber piece abuts against, controls the lateral position of the lumber piece on the feed conveyor. Numerous prior art arrangements for adjustable positioning fences for use with such a feed conveyor arrangement have been proposed in the past. For example a step positioning fence is disclosed in the published Canadian Patent application 2,241,481 of Wight et al. The stepped positioning fence of Wight has a plurality of rigid elevated faces, or steps that extend longitudinally along a side of the fence in an adjacent stepped array of differing offset spacing. The fence is oriented to present one of the steps for contact with the lumber piece to align the lumber end to the corresponding offset of that step. The lumber is urged into contact with the fence by the lateral alignment rollers resulting in alignment of the lumber end to the fence step offset. The stepped fence provides fixed incremental ending settings and a positioning mechanism to ensure the board is presented with a step suitable to obtain the desired or intended lateral translation of the board piece.
Another flexible trimmer position fence is disclosed in Canadian Patent 2,191,390 to Jackson, which discloses a board positioning fence comprised of a plurality of adjustable fence elements each staged one after the other in the downstream direction of travel of the lumber to be positioned. The lumber is urged against the positioning fence by lateral alignment or ending rollers. The ending rollers urge the lumber laterally across the feed conveyor into contact with the successive fence elements of the board positioning fence. When the desired lateral positioning of the board is achieved, lift skids are engaged to remove the lumber from contact with the lateral urging end rollers. This arrangement has multiple flexible fence elements, which are adjusted to allow the board to be ended to the desired positioning or ending location. Once the board has been displaced laterally to the desired position offset, skids are engaged that lift the positioned lumber piece away from the ending rollers.
Another arrangement to provide board lumber end positioning is disclosed in the Canadian patent 2,236,508 of Hannebauer et al. Hannebauer discloses a circulating paddle positioning fence with a flexible guide track. Actuators position the flexible guide track, which results in corresponding positioning of a paddle to a desired offset or ending position.
And yet another positioning mechanism is disclosed in the published Canadian Patent application 2,345,872 of Jobin, for apparatus for positioning pieces of wood for precise cutting. Jobin discloses an adjustable barrier, which is provided with actuators to position the barrier to the desired offset location. Various forms of adjustable barrier are shown including ones which have a face that remains perpendicular to the board as well as providing for incline planes that have a set displacement selected by an actuator to achieve an ending or offset of the lumber laterally to the desired offset amount.